Intergalactic neutral hydrogen gas in the Grus quartet of galaxies

Australia Telescope Compact Array multi-configuration mosaicing of
the Grus quartet of galaxies reveals the presence of spectacular
tidal structures. of neutral atomic hydrogen
(H i) gas, i.e. 11% of all H i in the group, are found to be
dragged from NGC 7582 into intergalactic space.
About of H i gas are contained in a tidal
tail emanating from the north-western disk of NGC 7582, with a projected
length of about 85 kpc and width of up to 32 kpc and a relative
velocity with respect to the centre of NGC 7582 of 130–140 km s-1.
of H i reside in an intergalactic H i cloud
48 kpc West of NGC 7582, which might originate from the disk of NGC 7582
as well and has no optical counterpart in a red Digital Sky Survey
(DSS) image.
These observations prove that tidal stripping is occurring in the
Grus quartet and that tidal features in compact groups can be
potentially important contributors of metal-enriched matter to the
intergalactic medium.
The tidal features around NGC 7582 cover an area of about 2000 kpc2,
almost doubling the group's cross-section for Lyman-α absorption
of light from background sources compared to the optical extent of the
member galaxies.

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